The present invention relates to an angular position measuring system. Specifically, the invention relates to angular position measuring systems used above all when large radii are used for the angular position measurement, e.g., for rotary tables or telescopes.
To measure the angular position, a graduated measuring tape, usually of steel, is fastened around the circumference of an object to be measured. If the measurement is to be performed over a full 360 degrees, care should be taken that, in the case of a measurement beyond the joint of the two ends of the measuring band, no measuring error results from a potentially existing space in the graduation.
In measuring angular position, it is known to insert a steel band having graduation marks into the groove of a graduation wheel and tension the steel band via a turnbuckle. See, e.g., xe2x80x9cDigitale Lxc3xa4ngen- und Winkelmexcex2technikxe2x80x9d [Digital Linear and Angular Measurement Technology], Alfons Ernst, Technical Library, Volume 165, Moderne Industrie Publishing House, 1998, pages 69-70. However, tensioning results in tangential frictional forces between the measuring tape and the graduated wheel on the periphery of the graduation wheel. Oftentimes, the frictional forces expand the measuring tape to different extents along its periphery, thereby potentially causing deviations in the angular position measurement. If one also wants to adjust the joint between the measuring tape ends such that there is no jump in the scanned signal at this point, the tension force is not to account for conditions such as centrifugal forces, but should instead correspond to the necessary adjusting force.
The present applicants"" prior application DE 19751019 A1 describes an angular position measuring system wherein a device is used to introduce the same tension force at both ends of the measuring tape. This results in a reduction in the angle error caused by irregular expansion or compression of the measuring tape as compared to systems wherein one end of the measuring band is fixedly connected to its base and a tension force is only exerted on the second end. It is further proposed to provide an elastic layer to reduce the friction between the measuring tape and the base. In the case of the proposed design approach, it is disadvantageous, on the one hand, that it cannot be used for systems that must measure a complete rotation around 360 degrees, and, on the other hand, that further force is exerted directly on the measuring tape by the clamping device. Thus, regions of the measuring tape having different expansions result due to the further occurrence of frictional forces.
It is the object of the present invention to provide an angular position measuring system having a measuring tape, where the joint adjustment of the ends of the measuring tape is largely independent of the mounting of the measuring tape on the body to be measured.
This object is achieved by an angular position measuring system for measuring a body to be measured. The system includes a measuring tape having an adjusting device for adjusting a joint between both ends of the measuring tape. It also has an elastic layer. The measuring tape is attached to the elastic layer. The elastic layer is elastic in at least a radial direction. The system also includes a clamping ring. The elastic layer is attached to the clamping ring. The clamping ring has a clamping device for attaching the measuring tape to the body to be measured.
The proposed angular position measuring system includes a measuring tape having a graduation, the measuring tape being attached via a layer, which is elastic in the radial and tangential direction, to a separate clamping ring. Advantageously, an adjusting device can be used to adjust both ends of the measuring tape already during the manufacture of this structure of clamping ring, elastic layer, and measuring tape. For assembly, this structure is then attached via the clamping ring to the body to be measured. In this context, tangential forces, which locally deform the clamping ring, do occur as a result of the friction between the clamping ring and the body surface. The elastic layer does not transfer this deformation or only transfers a small portion of the deformation to the measuring tape. During assembly, the joint adjustment need not be repeated. Both operations are independent. The cost of such an assembly is relatively low. It is understood that the joint can also be adjusted after the clamping ring is assembled. A further positive effect is that smaller deviations from the ideal shaft diameter can be compensated for by the elastic layer, e.g., in the case of attachment to a shaft. Thus, the demands on the workmanship of the shaft are reduced. The measuring tape is attached in a self-centering manner.